Thermal stability of Sm-TM high temperature magnets at 300-550°C

Investigation of thermal stability at 300-550°C for the newly developed Sm(Co_wFe_vCu_xZr_y) _z high temperature magnets is reported in this paper. Three factors are responsible for the irreversible losses at high temperatures. One factor is the loss associated with a nonlinear induction demagnetization curve. This results in significant loss when the magnet is exposed to temperatures higher than the maximum use temperature T_M. Another factor is the surface oxidation, which is more severe with increasing temperature and time at high temperature. Surface oxidation can be reduced by coating with a high temperature ceramic coating. The third factor is the result of metallurgical changes in the magnets. This loss is relatively small in the new magnets, which actually is <2% after 360 hours at 550°C. The experiment confirms that coated magnets with T_M UP to 550°C can be expected to have considerable life expectancy and relatively low losses at the intended T_M